Wave generating apparatus for study of wave phenomena

ABSTRACT

A wave generating apparatus particularly adapted for use in studying wave phenomena having a plurality of wave source means mounted above a ripple tank and reciprocated vertically by a pair of pivotally mounted parallel rocker arm means to produce waves in the surface of the fluid in the ripple tank. The means driving the rocker arms are adjustable with respect to the rocker arms to vary the amplitude of the waves produced and may be regulated by control means in electrical communication with them to vary the frequency and phase of the waves produced. The bottom of the ripple tank is sloped upwardly from its center to effectively damp the waves in at least one direction. The wave generator and ripple tank may be used in combination with an overhead projector or an overhead light source so that images of the waves produced are projected upon an easily visible plane surface.

United States Patent [191 Mazurek WAVE GENERATING APPARATUS FOR STUDY OFWAVE PHENOMENA [75] Inventor: Henry E. Mazurek, Glen Ellyn, Ill.

[73] Assignee: Cenco Incorporated, Chicago, Ill.

[22] Filed: Jan. 15, 1973 [21] Appl. N0.: 323,646

Ripple Tank, Complete 03-074950-6 page 24 of The Project Physics Course,A Descriptive Catalog from Sept. 24, 1974 I Holt, Rinehart and Winston,Recd Sept. 22, 1972.

Primary ExaminerHarland S. Skogquist Attorney, Agent, or Firm-Comer W.Walters [57] ABSTRACT A wave generating apparatus particularly adaptedfor use in studying wave phenomena having a plurality of wave sourcemeans mounted above a ripple tank and reciprocated vertically by a pairof pivotally mounted parallel rocker arm means to produce waves in thesurface of the fluid in the ripple tank. The means driving the rockerarms are adjustable with respect to the rocker arms to vary theamplitude of the waves produced and may be regulated by control means inelectrical communication with them to vary the frequency and phase ofthe waves produced. The bottom of the ripple tank is sloped upwardlyfrom its center to effectively damp the waves in at least one direction.The wave generator and ripple tank may be used in combination with anoverhead projector or an overhead light source so that images of thewaves produced are projected upon an easily visible plane surface.

12 Claims, 8 Drawing Figures SOURCE PAIENIEnsarzmu SHEEI 1 OF 2 POWERSOURCE Q (v w A .fR Wi: l

IHHHH WAVE GENERATING APPARATUS FOR STUDY OF WAVE PHENOMENA BACKGROUNDOF THE INVENTION This invention relates to an apparatus for generatingwaves of variable frequency, phase and amplitude for studying wavephenomena.

The use of wave generators as a teaching tool is well recognized. Suchgenerators are often used to produce waves allowing the students tostudy the phenomena of reflection, defraction, refraction andinterference in a laboratory setting. Previous generators, however, haveoften been limited in their use and desirability by their high cost andcumbersome construction, their lack of flexibility in performingmultiple source variations of the standard tests, and their inability toillustrate additional wave phenomena such as phase.

Recent constructions of wave generating apparatus are shown in relatedU.S. Pat. Nos. 3,253,353 and 3,276,614 to J. G. Steed et al. While Steedet al teach a device which provides for variation of the frequency andphase relationship of the point sources, this device still containsseveral undesirable disadvantages. The Steed et al apparatus is limitedto only two point sources, yet it is often desirable to have more thantwo point sources and to be able to vary the number of point sourceseasily. There is no suggestion in Steed et al of any means forincreasing the number of wave sources, since there is only a singlemotor. Further, Steed et al teach a complex mechanical means of varyingthe phase and speed of the motor, which is subject to abuse andbreakdown. In addition, wave images are projected below the ripple tankmaking observation by a large group or photographing difficult. Finally,there is no provision in the prior art of a means of damping waves toprevent reflections off the side of the ripple tank, or of easilyregulating the level of the fluid in the ripple tank.

DESCRIPTION OF THE INVENTION The present invention allows simultaneousvariation and control of the frequency, phase and amplitude of wavesgenerated from a variable number of point sources in a ripple tankconstructed to eliminate interference by waves reflected from the sidesof the tank. This invention overcomes the disadvantages of the prior artby a wave generator having vertical support means held in spacedrelationship by and supporting a horizontal support means which may bepositioned above a projecting screen of an overhead projector or below alight source. The vertical support means are bridged by a pair ofparallel rocker arms pivotal on them and extending along the length ofthe horizontal support means. Mounted on the horizontal support meansand below these rocker arms are a variable number of wave point sourcemeans upwardly biased against the bottom of the rocker arms and movablein a vertical reciprocal fashion upon pivotal movement of the rockerarms. The rocker arms are independently connected by drive means mountedon one vertical support to dual motor means, each of which drive one ofthe rocker arms.

The drive means includes a pair of rod means connected at their upperends to an outwardly extending flange on each rocker arm, and, at theirlower ends, to a ring moved by an eccentric driven by a pulley reductoprovide electrical control of the frequency of the waves by varying thespeed of the motor.

This invention, therefore, provides simple, yet novel means to controlphase, frequency and amplitude. It eliminates the complex mechanicalgearing previously required to vary these aspects of the waves. Thiswave generating apparatus is constructed so that it may be used incombination with an overhead projector to allow images of the wavesproduced to be projected on a plane surface, such as the wall, forphotographing and extended study of the various phenomena. The uniquelyconstructed ripple tank effectively clamps out secondary wavereflections from its walls because of its tapered bottom and allows easyvariation of the fluid level. The variable number of point sources madeavailable for use in the novel construction of this inventionsignificantly increases the number of experiments which may be conductedand eliminates the inflexibility of previous devices.

Accordingly, it is an object of this invention to provide a wavegenerating apparatus that is simple and inexpensive in construction andallows great flexibility in the number and types of experiments in whichit is useful.

It is another object of this invention to provide a wave generatingapparatus which allows electrical variation and control of the phase andfrequency of waves produced and mechanical variation and control of theamplitude of such waves.

It is a further object of this invention to provide a wave generatingapparatus which permits the use of a plurality of wave sources.

It is still another object of this invention to provide a wavegenerating apparatus which has an easily variable number of wave pointsources, any two groups of which may be varied in phase relationshipbetween zero and It is a still furtherobject of this invention toprovide a wave generating apparatus which is particularly useful inconnection with an overhead projector to project wave images on a planesurface.

It is also an object of this invention to provide a wave generatingapparatus having a ripple tank which substantially eliminates thesecondary reflection due to waves bounced off the walls of the tank.

It is also another object of this invention to provide a wave generatingapparatus having a ripple tank which allows the level of the fluid inthe tank to be easily varied.

These and other objects of this invention will become apparent from thefollowing description of the drawings illustrating a preferredembodiment wherein:

FIG. 1 is a perspective view of the wave generating apparatus of thisinvention as used in combination with an overhead projector;

FIG. 2 is a front elevational view of the wave generating apparatusshown in FIG. I;

FIG. 3 is a top view of the wave generator alone;

FIG. 4 is an end elevational view of the wave generator alone takengenerally along line 44 in FIG. 2;

FIG. 5 is a cross-sectional elevational view of the wave generator ofthis invention taken generally along line 5-5 of FIG. 2;

FIG. 6 is a schematic view of a possible embodiment of the control anddrive circuitry of the wave generating apparatus shown in FIG. 2;

FIG. 7 is a top plan view of the ripple tank shown in FIG. 2; and,

FIG. 8 is a cross-sectional end elevational view of the ripple tanktaken generally along line 88 of FIG. 7.

Referring now to the drawings and in particular to P10. 1, the wavegenerating appartus of this invention is shown generally at 10. Thiswave generating apparatus 10 is positioned for use in combination with aconventional overhead projector 12 having a horizontal projection screen13 and an image projecting means 15, normally including a number ofmirrors or lenses to rectify and project the focused image on a verticalscreen.

The wave generating apparatus 10 includes a wave generator 14 and aripple tank 16 which contains a fluid media, such as water, in whichwave phenomena may be produced.

The wave generator 14 has. at its opposite ends, vertical support meansor legs 18 which may be integrally molded of a sufficient length tosupport the wave generator 14 above the floor. Thus, the wave generator14 need not be mounted on the overhead projector and is easily movableso that it may be used with overhead light sources to project ahorizontal image, if desired. The vertical support legs I8 arepositioned on opposite sides of the rectangular ripple tank 16 and have,mounted between them, parallel horizontal support means or bars 20disposed in vertical alignment, one above the other, as shown moreclearly in FIG. 2.

A pair of rocker arms 22 and 24 are mounted in parallel relationship tothe horizontal bars 20, on pivotal connections 26 at either end of thevertical support legs 18. These rocker arms, which are disposed inmirrorimage relationship will be referred to as the first rocker arm 22and the second rocker arm 24, respectively. They are constructed ofangles disposed along the length of the support bars 20 and above thesupport bars, having at either end a centrally extending flange 27, asshown in FIG. 4, by which they may be mounted for pivotal movement withrespect to the vertical legs 18 and the horizontal bars 20 byconnections 26. The rocker arms 22 and 24 are disposed so that thedownwardlyextending leg of each angle is positioned to the outside toengage the top of the wave point sources 28, which reciprocate toproduce the desired waves in the fluid media.

As shown in FIGS. 1 and 2, each wave point source 28 includes a verticalplunger rod 30 which is held in a vertical position and mounted forreciprocal movement in a mounting block 32. The mounting block 32 isshaped so that is has an enlarged portion having a bore therethrough forreceiving the plunger 32, which extends beyond the edges of the lowerhorizontal bar 20, and a narrower body portion formed to fit in themounting space between the upper and lower horizontal support bars 20. Afastening means 34, such as a machine screw and large washer is disposedon the opposite side of this body portion, as shown in FIG. 2, to betightened against the sides of the upper and lower support bars 20 tofirmly mount each wave point source assembly 28 in position between thebars. At the lower end of the plunger 30 is mounted a foot 36, havingits bottom surface in contact with the surface of fluid 17. Thereciprocal movement of this foot 36 generates the waves in the fluid. Aspring 38 is disposed around the circumference of the plunger rod 30between the mounting block 32 and a retaining head 39 to urge theplunger rod 30 and attached foot 36 to an upward position.

It may be seen by reference to the drawings that the wave point sources28 may be mounted on opposite sides of the horizontal bars, if desired,and as many sources 28 as required in a particular experiment may bemounted along the length of the horizontal bars 20. This allows greatflexibility in choosing the number of sources in a particular experimentand also in choosing a particular fixed position or point from whicheach source may generate a wave. This flexibility of location enablesthe operator to generate a number of waves having their sources atdifferent points, both longitudinally and laterally of the ripple tank16.

The plungers 30 of the wave point sources 28 are moved in a reciprocalfashion to produce the desired waves by the pivotal movement of thefirst and second rocker arms 22 and 24, respectively. Thedownwardlyextending flange of each rocker arm engages the heads 39 ofthe wave point source 28 disposed on its particular side and, inpivoting about the connection 26, reciprocates the plunger 30 a slightdistance to create a disturbance on the fluid surface. This pivotalmovement of the rocker arms 22 and 24 is caused by thegenerallyreciprocal movement of the drive rods 42 and 42 which engagehorizontal and outwardly-extending rocker arm flanges 40 and 40 neartheir upper ends. This movement is caused by similar, but independentdual drive assemblies, operating each drive rod as wili be describedbelow.

Prime numerals are used to refer to parts of similar description in eachdrive assembly since each assembly has a similar construction andfunction. Only a single assembly will therefore be described. The driverod 42 may be moved outwardly or laterally with respect to the rockerarm 22 in a rocker arm adjusting slot 44 to permit variation of thelength of the lever arm used to move the rocker arm 22 around the pivotpoint 26. Outward movement will increase the length of this lever armand thus decrease the vertical component of movement of the flange andthe corresponding amplitude of the wave produced by movement of the wavesource 28. Conversely, inward movement of the drive rod 42 in slot 44will increase the amplitude of the wave. Whenever the drive rod 42 ismoved in adjusting slot 44, a drive rod head 46 may be moved upwardly ordownwardly on a threaded portion of drive rod 42 so that the rocker armflange 40 and rocker arm 22 are maintained in a horizontal position toassure accurate variation of amplitude.

The drive rod 42 is driven in reciprocal fashion by a drive assembly,shown generally at 48, which is mounted on a support means 50 which maybe mounted directly on vertical supports 18 or attached thereto by rigidmounting means 52, as shown in FIG. 2. The drive assembly 48 consists ofa direct current motor means 54 mounted near the bottom and outward ofthe support means 50. This motor means 54, upon actuation, rotates adrive pulley 56 around the central axis of the motor means. Drive pulley56 is connected by a belt 57 to a reduction pulley 58, which effectivelyreduces the direct rotational speed of the motor means 54 to a speedacceptable for use in this wave generating apparatus. The reductionpulley 58 is rotated about a central axis 59 by this arrangement.Mounted on the central axis 59, for rotation therewith, is an eccentric60. Disposed about the circumference of the eccentric 60 is a drive rodmounting ring 62, having a radial hole or bore formed at one point onits circumference. This hole or bore receives the lower end of the driverod 42 and holds it firmly in a fixed relationship. The drive rod 42also passes through a bore in a rod guide and adjusting means 66 nearits middle portion. This rod guide and adjusting means 66 is mounted onthe support means 50 in an amplitude adjusting slot 64 extendinglaterally of the support means 50 and the rocker arms 22 and 24, toassist in permitting lateral movement of the drive rod 42 to vary thelength of the lever arm of the rocker arm and thereby the amplitude ofthe waves produced. The rod guide and adjusting means 66 maintains rod42 in a set angular position with respect to the vertical axis throughcentral axis 59 while allowing rod 42 to move freely in a reciprocalfashion within it.

By this arrangement, the eccentric 60, as it rotates freely within thedrive rod mounting ring 62, will move the ring 62 upwardly or inreciprocal fashion as it makes a complete revolution, as shown in FIG.5, where motors 54 and 54' are approximately 180 out of phase, thuscausing the eccentric 60 and 60 and their respective drive rods to be inopposite positions.

In addition to mechanical control of the amplitude, control of the phaseand frequency are accomplished by control of the motor means 54 and 54'by a simple circuit of the type shown in FIG. 6. This electrical circuitincludes a 3 to 6 volt battery 70 in electrical communication bysuitable electrical conduit means 71 through one terminal with arheostat 72 connected in series with the motors 54 and 54' and variableto increase or decrease their speed and thus the frequency of the wavefronts produced. The other terminal of battery 70 is connected byconduit means 71 to a similar rheostat 74 which is connected between orin parallel with the motors 54 and 54 vary the current and power in eachmotor circuit and thus the phase of the waves. If rheostat 74 is movedso that the resistances in each motor circuit are equal, the motors willrun in phase. In this condition. the lines of interference formed bywaves from more than one point source will appear to be stationary.Ifthe resistances are made unequal, however, the interference lines willbegin to rotate. Rotation will appear to occur in the direction of thepoint sources reciprocated by the motor receiving the most power.

The ripple tank 16 is shown in detail in FIGS. 7 and 8. It is formed ofcontinuous side walls 78 which are fluid-tightly joined to a bottom wall80. The bottom wall 80 is sloped upwardly from its center point so thatwaves moving toward the short or lateral sides of the tank will beeffectively damped out and not create reflected interference waves whichwould interfere with the conduct and observation of the experiment. Thetank 16 is preferably rectangular to permit extended travel of a wave inone direction to allow observation of its motion. It is clear that thetank 16 could also be formed of a continuous circular side wall having afrusto-conical shaped bottom wall fluid-tightly sealed to it. A trough81 is formed out of one section of the bottom wall so that the bottom ishorizontal in that particular section. This allows water to be easilyevacuated from the tank to a liquid reservoir, so that by verticalmovement of the liquid reservoir, the level of liquid in the tank 16 maybe raised or lowered without having to add or drain water from theripple tank itself. The level of the fluid media 17, however, shouldalways be approximately at or below the intersection ofthe side andbottom walls if effective damping is to be achieved.

The foot 36 of each wave point source 28 is preferably not actuallyimmersed in the fluid 17, and does not break the surface of the fluid inits upward movement. The wave point sources 28 and the feet 36 should bepositioned with respect to the surface of the fluid 17 so that the foot36 contacts the surface in its lowest position. Thus, when the plunger30 and foot 36 are reciprocated slightly upward by the action of thedrive assembly and the resulting pivotal movement of the rocker arms,the tendency of the fluid used, such as water, to adhere to the broadbottom surface of the foot 36 will create a sufficient disturbance tocause a wave, yet not a great enough distrubance to disrupt the wavepattern or produce undesirable results.

The materials which may be used in constructing this invention includeany suitable material which may be easily cleaned, resists corrosion,and may be formed or bored as desired including brass, aluminum, steeland steel alloys.

While this invention has been described in relation to preferredembodiments thereof, it will be apparent to those skilled in the artthat the structural details are capable of wide variation withoutdeparting from the principles of the invention.

I claim:

1. A wave generating apparatus particularly adapted for use in studyingwave phenomena including a tank means adapted to receive a liquid, awave generator having a first support means, second support means joinedto said first support means in spaced relationship above said liquid insaid tank means, rocker arm means mounted on and between said firstsupport means for pivotal movement relative to said first support means,wave source means mounted on said second support means and disposed foroperative engagement with said rocker arm means thereby to bereciprocally moved on movement of said rocker arm means, said wavesource means having one end disposed for engagement-with said liquid,drive means operatively engaging said rocker arm means to pivotally movesaid rocker arm means, control means to regulate the operation of saiddrive means and the movement of said rocker arm means, said tank meansincluding side walls and a bottom wall sloping upwardly from its centerand joined in fluid-tight relationship thereto and containing saidliquid therein, said wave generator being operable to produce waves insaid liquid which may be varied in frequency, phase and amplitudeaccording to the operation of said control means and adjustment of saiddrive means.

2. The wave generating apparatus of claim 1 wherein said control meansincludes dual direct current motors, each of which is operativelyconnected to corresponding drive means to move said drive meansindependently to thereby cause said rocker arm means to move withrespect to said second support means.

3. The wave generating apparatus of claim I wherein said second supportmeans includes horizontal bar means disposed in spaced relationship todual rocker arms disposed in parallel relationship along said bar meanson opposite sides thereof, each of said rocker arms being pivotal withrespect to said bar means to move certain of said wave source meansmounted thereon, said wave source means including at least one plungerreciprocally movable with respect to said bar means in the liquidcontained in said tank means to create a point disturbance therein.

4. The wave generating apparatus of claim 1 wherein said wave sourcemeans includes a plurality of individual plungers mounted on said secondsupport means and disposed along the length thereof for verticalreciprocal movement with respect thereto, one end of each of saidplungers being biased into contact with said rocker arm means such thatupon pivotal movement of said rocker arm means, said plunger is moved inthe liquid contained in said tank means to create a point sourcedisturbance therein, said plungers being mountable on opposite sides ofsaid second support means as desired, such that variation in the phaseof the waves produced thereby may be obtained upon movement of saidrocker arm means as regulated by said control means.

5. The wave generating apparatus of claim 1 wherein said drive meansincludes dual, independent pulley reduction means rotatably mountedadjacent one another on said first support means, each of said reductionmeans having eccentric means mounted at the central axis thereof forrotation therewith, said eccentric means supporting one end of anupwardly-extending rod means, and, upon rotation of said reductionmeans, acting to move said rod means reciprocally relative to saidsecond support means, said rod means being operatively engaged, near itsupper end, with said rocker arm means such that movement of said rodmeans will cause said rocker arm means to be pivoted with respect tosaid second support means to move said wave source means.

6. The wave generating apparatus of claim 2 wherein said control meansincludes variable resistance means placed between said dual motor meanssuch that when resistance is varied to decrease the electrical powersupplied to one of said motor means, the electrical power supplied tothe other of said motor means is correspondingly increased, anydifferences in electrical power supplied to the motor means causing thespeeds of the respective motor means to vary proportionately, therebyvarying the degree of phase between the waves produced by the drivemeans, rocker arm means and wave source means mechanically connected toand operated by the motor means.

7. The tank means of claim 1 wherein said side walls are integrallyformed with said bottom wall, said bottom wall additionally having atrough means formed in its surface. said trough means having a generallyflat bottom and being effective to allow the liquid level in the tank tobe varied through an outlet means in communication with an outsideliquid reservoir.

8. The wave generating apparatus of claim 1 wherein a portion of saiddrive means is movable laterally relative to said second support meansand said rocker arm means to vary the amplitude of waves produced bysaid wave generating apparatus.

9. The wave generating apparatus of claim 5 wherein each of said rodmeans is maintained in a generally upright position and in operativeengagement with said eccentric means by holding means, said rod meansbeing laterally movable with respect to said rocker arm means in slotsformed in said first support means and said rocker arm means such thatwhen said rod means is moved outwardly within said slots relative tosaid rocker arm means, the point of engagement of said rod means andsaid rocker arm means is moved outward on said rocker arm means relativeto said second support means, thereby decreasing the amplitude of thewaves produced by operation of the wave generating apparatus.

10. A wave generating apparatus particularly adapted for use with anoverhead projector, including a wave generator positioned above theprojection screen of the projector having vertical support meansextending above the plane of the screen thereof, horizontal supportmeans mounted on said vertical support means above the projectionscreen, rocker arm means mounted on said vertical support means forpivotal movement with respect to said vertical support means, wavesource means mounted on said horizontal support means, and disposed inoperative engagement with said rocker arm means to be reciprocally movedthereby, drive means moved by motor means and operatively engaging saidrocker arm means to pivotally move said rocker arm means, said motormeans being regulated in operation by control means, and including tankmeans disposed between the projection screen and said horizontal supportmeans, said tank means having side walls and a bottom wall slopingupwardly from its center and joined in fluid-tight relationship thereto,said tank means containing a liquid such that upon movement of saiddrive means, said wave source means are moved reciprocally with respectto the surface of said liquid to produce waves in said liquid which maybe varied in frequency, phase and amplitude by operation of said controlmeans and adjustment of said drive means.

11. The wave generating apparatus of claim 10 wherein said verticalsupport means are disposed at opposite ends of said horizontal supportmeans and are removably mounted on opposite sides of the projectorscreen, one of said vertical support means having a plate supportingsaid motor means and said drive means, said motor means beingoperatively connected to said drive means to move said drive means.

12. A wave generator providing for the simultaneous control of thephase, frequency and amplitude of waves produced thereby, includingfirst support means, second support means joined to said first supportmeans and maintained in spaced relationship above the surface of aliquid medium for the production of waves thereby, rocker arm meansmounted on said first support means for pivotal movement relative tosaid first support means, wave source means mounted on said secondsupport means and disposed for operative engagement with said rocker armmeans, said wave source means having one end disposed for engagementwith said liquid, drive means operatively engaging said rocker arm meansand operable to pivotally move said rocker arm means thereby toreciprocally move said wave source means, said drive means beingadjustable relative to said second support means to vary theamplimovement of said rocker arm means and thereby vary tude of thewaves produced by movement of said wave the phase and frequency of wavesproduced by said source means relative to said liquid, and control meanswave generator to regulate the operation of said drive means and the

1. A wave generating apparatus particularly adapted for use in studyingwave phenomena including a tank means adapted to receive a liquid, awave generator having a first support means, second support means joinedto said first support means in spaced relationship above said liquid insaid tank means, rocker arm means mounted on and between said firstsupport means for pivotal movement relative to said first support means,wave source means mounted on said second support means and disposed foroperative engagement with said rocker arm means thereby to bereciprocally moved on movement of said rocker arm means, said wavesource means having one end disposed for engagement with said liquid,drive means operatively engaging said rocker arm means to pivotally movesaid rocker arm means, control means to regulate the operation of saiddrive means and the movement of said rocker arm means, said tank meansincluding side walls and a bottom wall sloping upwardly from its centerand joined in fluid-tight relationship thereto and containing saidliquid therein, said wave generator being operable to produce waves insaid liquid which may be varied in frequency, phase and amplitudeaccording to the operation of said control means and adjustment of saiddrive means.
 2. The wave generating apparatus of claim 1 wherein saidcontrol means includes dual direct current motors, each of which isoperatively connected to corresponding drive means to move said drivemeans independently to thereby cause said rocker arm means to move withrespect to said second support means.
 3. The wave generating apparatusof claim 1 wherein said second support means includes horizontal barmeans disposed in spaced relationship to dual rocker arms disposed inparallel relationship along said bar means on opposite sides thereof,each of said rocker arms being pivotal with respect to said bar means tomove certain of said wave source means mounted thereon, said wave sourcemeans including at least one plunger reciprocally movable with respectto said bar means in the liquid contained in said tank means to create apoint disturbance therein.
 4. The wave generating apparatus of claim 1wherein said wave source means includes a plurality of individualplungers mounted on said second support means and disposed along thelength thereof for vertical reciprocal movement with respect thereto,one end of each of said plungers being biased into contact with saidrocker arm means such that upon pivotal movement of said rocker armmeans, said plunger is moved in the liquid contained in said tank meansto create a point source disturbance therein, said plungers beingmountable on opposite sides of said second support means as desired,such that variation in the phase of the waves produced thereby may beobtained upon movement of said rocker arm means as regulated by saidcontrol means.
 5. The wave generating apparatus of claim 1 wherein saiddrive means includes dual, independent pulley reduction means rotatablymounted adjacent one another on said first support means, each of saidreduction means having eccentric means mounted at the central axisthereof for rotation therewith, said eccentric means supporting one endof an upwardly-extending rod means, and, upon rotation of said reductionmeans, acting to move said rod means reciprocally relative to saidsecond support means, said rod means being operatively engaged, near itsupper end, with said rocker arm means such that movement of said rodmeans will cause said rocker arm meaNs to be pivoted with respect tosaid second support means to move said wave source means.
 6. The wavegenerating apparatus of claim 2 wherein said control means includesvariable resistance means placed between said dual motor means such thatwhen resistance is varied to decrease the electrical power supplied toone of said motor means, the electrical power supplied to the other ofsaid motor means is correspondingly increased, any differences inelectrical power supplied to the motor means causing the speeds of therespective motor means to vary proportionately, thereby varying thedegree of phase between the waves produced by the drive means, rockerarm means and wave source means mechanically connected to and operatedby the motor means.
 7. The tank means of claim 1 wherein said side wallsare integrally formed with said bottom wall, said bottom walladditionally having a trough means formed in its surface, said troughmeans having a generally flat bottom and being effective to allow theliquid level in the tank to be varied through an outlet means incommunication with an outside liquid reservoir.
 8. The wave generatingapparatus of claim 1 wherein a portion of said drive means is movablelaterally relative to said second support means and said rocker armmeans to vary the amplitude of waves produced by said wave generatingapparatus.
 9. The wave generating apparatus of claim 5 wherein each ofsaid rod means is maintained in a generally upright position and inoperative engagement with said eccentric means by holding means, saidrod means being laterally movable with respect to said rocker arm meansin slots formed in said first support means and said rocker arm meanssuch that when said rod means is moved outwardly within said slotsrelative to said rocker arm means, the point of engagement of said rodmeans and said rocker arm means is moved outward on said rocker armmeans relative to said second support means, thereby decreasing theamplitude of the waves produced by operation of the wave generatingapparatus.
 10. A wave generating apparatus particularly adapted for usewith an overhead projector, including a wave generator positioned abovethe projection screen of the projector having vertical support meansextending above the plane of the screen thereof, horizontal supportmeans mounted on said vertical support means above the projectionscreen, rocker arm means mounted on said vertical support means forpivotal movement with respect to said vertical support means, wavesource means mounted on said horizontal support means, and disposed inoperative engagement with said rocker arm means to be reciprocally movedthereby, drive means moved by motor means and operatively engaging saidrocker arm means to pivotally move said rocker arm means, said motormeans being regulated in operation by control means, and including tankmeans disposed between the projection screen and said horizontal supportmeans, said tank means having side walls and a bottom wall slopingupwardly from its center and joined in fluid-tight relationship thereto,said tank means containing a liquid such that upon movement of saiddrive means, said wave source means are moved reciprocally with respectto the surface of said liquid to produce waves in said liquid which maybe varied in frequency, phase and amplitude by operation of said controlmeans and adjustment of said drive means.
 11. The wave generatingapparatus of claim 10 wherein said vertical support means are disposedat opposite ends of said horizontal support means and are removablymounted on opposite sides of the projector screen, one of said verticalsupport means having a plate supporting said motor means and said drivemeans, said motor means being operatively connected to said drive meansto move said drive means.
 12. A wave generator providing for thesimultaneous control of the phase, frequency and amplitude of wavesproduced thereby, including first support means, second support meansjoIned to said first support means and maintained in spaced relationshipabove the surface of a liquid medium for the production of wavesthereby, rocker arm means mounted on said first support means forpivotal movement relative to said first support means, wave source meansmounted on said second support means and disposed for operativeengagement with said rocker arm means, said wave source means having oneend disposed for engagement with said liquid, drive means operativelyengaging said rocker arm means and operable to pivotally move saidrocker arm means thereby to reciprocally move said wave source means,said drive means being adjustable relative to said second support meansto vary the amplitude of the waves produced by movement of said wavesource means relative to said liquid, and control means to regulate theoperation of said drive means and the movement of said rocker arm meansand thereby vary the phase and frequency of waves produced by said wavegenerator.